Within the scope of the work, we investigate the photoelectrochemical properties of chemically deposited bismuth oxysulfide films (BOS) in a dimethyl sulfoxide (DMSO) solution of quinhydrone. The films demonstrate an appearance of a cathodic photocurrent under negative electrochemical polarization and high external quantum efficiency (EQE) values up to 340%. The electrochemical potential window of BOS films, they can operate, is very broad and comprises from −1.0 to 1.7 V vs. standard hydrogen electrode (SHE). The detailed investigation of BOS films with XRD, SEM, EDX and XPS shows the absence of any changes in the phase composition, morphology, bulk, and surface elemental composition of the BOS film after photoelectrochemical impact for half of the year. The photoelectrochemical results were used to design of UV–Vis-NIR photodetector, which has a responsivity up to 1.2 A/W at 465 nm. This value significantly exceeds the previously reported responsivity values for bismuth oxysulfide based photodetectors.

Electrooxidation of rhodamine B acylhydrazone in MeCN involves free radical intermediates and yields diverse products.

Bismuth oxysulfide (BOS) films were formed on dielectric glass substrates by the chemical bath deposition. They have a high sensitivity to moisture content and demonstrate the decrease in the electrical resistance up to three orders of magnitude when the relative humidity reaches 85% and more. The high sensitivity of resistive structure representing 0.65 & mu;m thick film between two Ag contacts is associated with randomly oriented thin nanoplate crystals. The presence of a great number of intergrain boundaries restricts electron transport (both in the dark and under illumination), which is desirable for resistive humidity sensors. The BOS films possess a high surface-to-volume ratio making them ultra-sensitive to adsorption of water. It is supposed that ionic conductivity in a thin layer of adsorbed water plays a crucial role in fast response of sensing structure (1-3 s) to adsorption-desorption cycles. High dark resistance and low photoconductivity of BOS films make them practically insensitive to processes of molecular oxygen adsorption and action of light when they are used as humidity sensing structure.

Cyclic voltammetry, UV-Vis absorption spectroscopy, and electron spin resonance are applied to study the properties of indotricarbocyanine dyes and their radicals formed during electrooxidation. We use electrochemistry to generate relatively stable free radicals of the dyes under controlled conditions. The dyes undergo electrooxidation during the chronoamperometric electrolysis at 1.1 V (versus saturated calomel electrode) yielding radical dications. The radicals exhibit an absorption band that is blue-shifted relative to the parent dye (561 nm versus 714 nm). In acetonitrile solutions, the radicals are characterized by a lifetime of ca. 20 min and a g factor of 2.002. The oxidation potential of the dyes is slightly greater than that of bromide ions allowing the radicals of the dyes to interact with bromide ions. The ability of the indotricarbocyanine dyes to sensitize generation of highly reactive bromine radicals might play an important role in their photodynamic activity.

Strong room temperature exciton photoluminescence (PL) has been observed in copper (I) oxide films electrochemically deposited in a tartrate electrolyte. The PL intensity of these films is two orders of magnitude higher than that of films deposited from the classical lactate electrolyte. X-ray diffraction (XRD) and Raman spectroscopy analyses demonstrate that the films prepared using tartrate electrolyte are characterized by higher grain size, which reduces a non-radiative recombination of charge carriers. Better optical quality of the Cu2O films prepared using tartrate electrolyte is explained taking into account stronger tartrate-copper complexes, which results in lower density of grain boundaries in such films. Moreover, higher buffering capacity of the tartrate complex provides stability of pH value in the diffusion layer of the near-electrode space preventing defect formation. Our study demonstrates the promise of using Cu2O films deposited from tartrate solution for solar energy applications like photoelectric energy conversion, hydrogen production, and photocatalysis.

The method of chemical deposition of monocrystalline bismuth thioiodide BiSI needles with a high quantum efficiency of photocurrent generation (up to 55 %) in aqueous solutions of electrolytes has been developed. It was revealed that the introduction of sulfide and iodide anions into the electrolyte solution leads to an increase of the absolute photocurrent values, as well as the presence of sulfide ions causes the significant (about 0.5 V) shift of BiSI bands energy towards more negative electrode potentials. The observed effect is of interest for increasing the photovoltage of solar cells based on BiSI and can find application in heterogeneous sensitized systems for increasing the efficiency of photoelectrons injection from a narrow-band sensitizer into a matrix of a wide-bandgap semiconductor.

Bismuth oxysulfide (BOS) films demonstrate giant incident photon-to-current conversion efficiency (IPCE >> 100%) under cathodic polarization. Their photoelectrochemical behavior and corrosion stability in aqueous solutions containing different redox systems ([Fe(CN)(6)](3-)/[Fe(CN)(6)](4-), Fe3+/Fe2+, I-2/I-, S-n(2-)/S2-) has been investigated. We established that the chemical stability of the BOS is controlled mainly by three factors: i) potentials of cathodic and anodic destruction of the BOS (Bi3+ reduction and S2- oxidation)L ii) protolytic reactions leading to the dissolution of the semiconductor in acidic solutions at pH<3; iii) presence in solutions of anions, capable to participate in ion exchange reactions with the semiconductor forming poorly soluble compounds (K[BiFe(CN)(6)]3H(2)O, BiOI and Bi2S3). The enrichment of the BOS surface with sulfur atoms (formation of S-terminated surface) gives rise to the substantial increase in the electrocatalytic activity of [Fe(CN)(6)](3-) cathodic reduction, which is accompanied by up to order increase of IPCE.

It was demonstrated in our previous work that the photoelectrochemical (PEC) reduction processes occur with a giant incident photon-to-current conversion efficiency (IPCE ≫ 100%) at bismuth oxysulfide (BOS) semiconductor films in aqueous solutions containing acceptors of photoelectrons ([Fe(CN)6]3-). The anomalously high IPCE was related to the photoconductivity of the semiconductor. In this work, we analyze the dynamics of the chemical and phase composition of BOS films with variation of their deposition time, as well as the dependence of photocurrent on the film thickness and wavelength of the incident light. We demonstrate that in the case of illumination with a short-wavelength light (λ = 465 nm), the photocurrent is reduced down to a complete disappearance with an increase in the film thickness in the range of 0.3-1.3 μm, and for a fixed thickness of the bismuth oxysulfide film, the photocurrent decreases with the reduction of the wavelength indicating that photogeneration of the charge carriers over the entire thickness of the film is necessary for the giant IPCE effect. Using the light induced transient grating (LITG) method, the lifetime of the charge carriers (τ) was determined in the range of 25-80 ps depending on the film thickness, whereas the diffusion coefficient (D) does not exceed 1 cm2 s-1 meaning that the charge transport across the films is determined only by drift.

Nanostructured layered bismuth oxysulfide films synthesized by chemical bath deposition reveal a giant incident photon-to-current conversion efficiency (IPCE). This study shows that surprisingly for the cathodic photocurrent in the photoreduction process, the IPCE reaches ≈2500% in aqueous solutions containing [Fe(CN)6 ]3- . The giant IPCE is observed starting from a certain minimal oxidizer concentration (c > 10-3 m for [Fe(CN)6 ]3- ) and decreases nonlinearly with an increase of illumination intensity. Giant IPCE is determined by the decrease in resistivity of the bismuth oxysulfide film under illumination with photoconductivity gain, which provides the possibility of charge carriers from an external circuit to participate in the photoreduction process. Giant IPCE is observed not only in [Fe(CN)6 ]3- solutions, but also in electrolytes containing other photoelectron acceptors: Fe3+ , I3- , quinone, H2 O2 . In all, solution-processed layered bismuth oxysulfide films offer large-area coverage, nontoxicity, low cost, and compatibility with a wide range of substrates. Abnormally high photoelectrochemical activity, as well as a band gap energy value favorable for efficient conversion of solar light (1.38 eV, direct optical transitions), proves the potential of bismuth oxysulfide photoelectrodes for a new generation of high-performance photoconverters.

A method of tin oxide(IV) — graphene oxide (GO) composite film electrodes preparation has been developed. GO sol was prepared by a two-stage oxidation of graphite and codeposited with tin(IV) oxide on a conducting substrate by dip coating. GO content increase up to 40 % resulted in the electroactive electrode surface enhancement, but the further increase in GO content caused an inverted effect. The electrodes were characterized by high electrocatalytic activity in anodic oxidation of CI anions in concentrated aqueous solutions of alkali metal chlorides. A significant effect of the metal cation was observed in the anodic reaction. Graphene oxide cathodic reduction on tin oxide(IV) — GO electrodes in LiCI solution in acetonitrile was accompanied by Li + cathodic reduction that activated the cathodic reduction of GO.

SnO2/GO (GO is graphene oxide) composite films with GO mass fraction w(c) ranging from 0.01 to 80% have been prepared using colloidal solutions. Heat treatment of SnO2/GO films in Ar atmosphere at 400 degrees C leads to GO reduction accompanied by partial exfoliation and decreasing of the particle thickness. SnO2/rGO (rGO is reduced GO) film electrodes demonstrate a high electrocatalytic activity in the anodic oxidation of inorganic (iodide-, chloride-, sulfite-anions) and organic (ascorbic acid) substances. The increase of the anodic current in these reactions is characterized by overpotential inherent to the individual rGO films and exchange current density grows linearly with rGO concentration at w(c) <= 10% indicating that the rGO particles in composites act as sites of electrochemical process. The SnO2/rGO composite films, in which the chemically stable oxide matrix encapsulates the rGO inclusions, can be considered as a promising material for applied electrochemistry. (C) 2015 Elsevier B.V. All rights reserved.